Notice that IDC's report focuses on PC processors – not merely processors in general. It doesn't take into account all those ARM-based processors that are already powering tablets and smartphones.

"While media tablets are a competitive factor at the system level because of competition for share of consumer wallets vs PCs," the report's author, Shane Rau, told The Reg in an email exchange. "Media tablets are not PCs in IDC's taxonomy, and the processors inside them are not PC processors. I define a PC processor by the design intent of the manufacturer."

And IDC sees that design intent of ARM-based processor manufacturers aimed squarely at Intel's turf – just as AMD, newly revitalized with its Fusion line of accelerated processing units (APUs), is aiming to grab a larger stake in the PC-processor marketplace.

ARM-processor manufacturers are starting small in their PC ambition. As Rau told us, "While there are some ARM-based netbooks (which are called mini-notebooks in IDC's taxonomy and are part of the PC taxonomy), the volumes are very small."

We asked Rau whether Microsoft's plan to port Windows 8 to ARM was a major reason for his projection of a 13 per cent ARM PC-processor market share in a mere four years, he agreed. "Yes," he answered. "Windows 8 moving to ARM is the major assumption in the long-term forecast for ARM in PCs. As Nvidia, Qualcomm, and TI announced at CES, they'll support Windows 8 with ARM-based SoCs, so that's a clear sign of intent to design for PCs and so the market direction."

Rau's "yes", however, was followed by a big ol' "but". "Other factors include ARM architectures that support PC functionality (with features like 64-bit processing, 64-bit memory addressing, high-speed interfaces, and large caches) and PC applications coming from ISVs," he cautioned. "If any major part of the necessary ecosystem for PCs falters, then ARM in PCs will falter. This is a long-term roadmap."

In other words, yes, Intel does face a challenge from the lower-power end of the PC-processor market, but a lot of independent ducks must line up in their correct rows for Chipzilla to feel major pain.

What's more, Wednesday's announcement of Intel's "tri-gate" 22nm processors may portend a better power/performance future for a company that has been late to the low-power, high-performance game.

That said, as Intel moves down the power ladder, ARM-based processors such as Nvidia's quad-core ARM Cortex-A9 Kal-el are moving up the performance rungs. And then there are those muscular ARM Cortex-A15 parts scheduled for late 2012 or early 2013.

Thing haven't been so much fun in the world of PC processors since Motorola/IBM/Freescale's PowerPC dropped out of the mêlée some years back. ®